I. Technical Field
The present invention relates to a method of cleaning a support plate that is attached to and supports a substrate, to thin the substrate.
II. Description of the Related Art
In recent years, there has been an increasing demand for higher integration and reduction in size and thickness of semiconductor chips to be mounted on electronic devices. Accordingly, the substrate that is a base of such semiconductor chips must be thinned, by grinding the substrate. However, this grinding weakens the strength of the substrate. This tends to crack and warp the substrate. Further, because a thinned substrate cannot be transferred automatically, such a substrate needs to be manually transferred. Therefore, handling of such a substrate cumbersome.
In order to solve this problem, a method for preventing the occurrence of cracking and warping of a substrate has been developed. According to the method, the substrate to be ground is attached to a glass support plate by use of an adhesive so that the strength of the substrate is maintained (See Japanese Patent Application Publication, Tokukai, No. 2005-191550 A (Publication Date: Jul. 14, 2005)).
However, in the method described in Japanese Patent Application Publication, Tokukai, No. 2005-191550 A (Publication Date: Jul. 14, 2005), in a case where a substance, such as an organic substance, is adhered to the support plate, a small gap is produced between the substrate and the support plate. This damages the substrate. Therefore, as pretreatment prior to attachment of the substrate, it is necessary to clean the support plate.
Typically, a support plate has a surface area that is equal to or more than a surface area of a substrate. Accordingly, if wirings are formed on the substrate being supported by such a support plate, metal sticks to an exposed peripheral portion of the support plate that is not covered by the substrate. Further, an adhesive remains on the support plate after the substrate is separated from the support plate. Therefore, for reusing the support plate, a substance such as metal and/or an organic substance that adheres to the support plate needs to be completely removed from the support plate after the substrate is separated from the support plate.
In general, metal and/or an organic substance each of which is adhered to a support plate can be removed by using a chemical such as acid, alkali, and/or an organic solvent. For example, the metal can be removed by use of aqua regia. Meanwhile, the organic substance can be removed by use of an organic solvent or acid.
As a method of cleaning a glass substrate, Japanese Patent Application Publication, Tokukaihei, No. 9-227170 A (Publication Date: Sep. 2, 1997) discloses a method according to which metal and/or an organic substance that is adhered to the glass substrate is removed by treating the glass substrate by use of a mixture of heated sulfuric acid and hydrogen peroxide solution.
Japanese Patent Application Publication, Tokukaishou, No. 62-235236 A (Publication Date: Oct. 15, 1987) discloses a method according to which a substance adhering a glass substrate is removed by cleaning the glass substrate by use of acid.
Further, Japanese Patent Application Publication, Tokukaishou, No. 63-180393 A (Publication Date: Jul. 25, 1988) discloses a method for removing a metal film. According to this method, when a metal film formed on a circuit substrate is melted and removed by laser light irradiation onto the metal film, a portion to be a target of the laser light irradiation is covered by liquid that transmits laser light so that the circuit substrate is not damaged due to heat of the laser light.